The present invention relates to a method of controlling valve landing in a camless engine which uses current and rate of change of current in an electronic valve actuator with discrete position sensors to calculate valve velocity for controlling valve landing.
Camless engine unthrottled operation enabled by fully actuated valves holds promise for improved fuel economy and drivability. Before this technology becomes production feasible, a number of technical problems need to be resolved. One of the key problems is associated with controlling the contact velocities in the valve actuation mechanism so that a reliable performance without unacceptable noise and vibrations is attained. This problem is often referred to as the soft landing problem (i.e., soft landing of the valve and actuation mechanism at its fully open and fully closed positions).
In a typical electromechanical actuator, the valve motion is affected by the armature that moves between two electromagnetic coils biased by two springs. The valve opening is accomplished by appropriately controlling the lower coil, while the upper coil is used to affect valve closing. High contact velocities of the armature as well as of valve seating may result in unacceptable levels of noise and vibrations. On the other hand, if the coils are not appropriately controlled, the valve landing may not take place at all, thereby resulting in engine failure.
Because the combustion processes in the engine that determine the magnitude of the disturbance force on the valves are stochastic, the disturbance force may vary from cycle-to-cycle. Consequently, a control system that determines the parameters of the coil excitation must combine both in-cycle compensation for the particular disturbance force profile realized within the present cycle, and slower cycle-to-cycle adaptation of the parameters of the excitation, that compensate for engine and actuator assembly aging as well as various other parameter variations.
The solutions proposed in the prior art either do not rely on armature position measurement at all, or they require a position sensing mechanism which continuously senses the location of the valve at all positions. The solutions without a position sensor may not be robust enough as they typically rely on open loop estimation schemes that would be rendered invalid should the engine or actuator assembly parameters change. The main problems with the solutions that rely on a continuous position sensor are the high cost and lack of reliability as the sensor may become inaccurate in the course of operation due to calibration drift.
Accordingly, it is desirable to provide an improved method and system for controlling valve landing in camless engines.
The present invention provides an improvement over prior art methods of controlling valve landing by using discrete position measurements and estimating valve velocity at these discrete locations based upon current and rate of change of current in an electronic valve actuator. The discrete position measurements are provided, for example, by switch-type position sensors. Specific examples of switch-type position sensors include optical (LED and photo-element based) sensors and magnetic pickup sensors. The number of position sensors could vary within the scope of the present invention, but preferably only three sensors are used to minimize cost.
Accordingly, the present invention provides a method of controlling valve landing in a camless engine including a valve movable between fully open and fully closed positions, and an electromagnetic valve actuator (EVA) for actuating the valve. The method includes providing at least one discrete position measurement sensor to determine when and if the valve is at a particular position during valve movement. The velocity of the valve at the particular position is estimated based upon current and rate of change of current in the electromagnetic valve actuator when the valve is at the particular position. Valve landing is then controlled based upon the estimated velocity.
In a preferred embodiment, three discrete position sensors are provided: with one sensor at the half-way point between fully open and fully closed positions, and the second and third sensors positioned near the fully open and fully closed positions.
Accordingly, an object of the invention is to provide an improved method of controlling valve landing in a camless engine which uses discrete position measurements in conjunction with current and rate of change of current in an electronic valve actuator for calculating velocity at the discrete locations, and thereby controlling valve landing.
The above object and other objects, features, and advantages of the present invention are readily apparent from the following detailed description of the best mode for carrying out the invention when taken in connection with the accompanying drawings.